Feedback Carburetor Actuator (FBCA)
The FBCA controls air/fuel ratio on signal from the ECA by adjusting the position of a vacuum bleed metering rod in the carburetor. This actuator is not a solenoid but a combination motor and leadscrew. The leadscrew changes the rotary motion of the motor to a linear (in and out) motion of the actuator shaft.
The FBCA actuator shaft can be set by ECA signal to any position between fully retracted and fully extended. When the actuator shaft is fully extended, the vacuum bleed metering rod is seated, permitting the slightly rich mixture to enter the engine unchanged.
When the actuator shaft is retracted, the metering rod bleeds vacuum from the control vacuum chamber into the fuel bowl. This lowers the air pressure in the fuel bowl, which leans out the air/fuel mixture.